When stacking chips, there are essentially two ways that chip to chip connections can be formed. One way, is to form the complete stack and then concurrently subject the entire stack to the conditions, such as heating and cooling, required to cause the electrically conductive bonding materials to establish the conductive path. The other way is to sequentially connect two components together, through heating and cooling of the connection points, and then sequentially attaching the next chip in the same manner, and so on, until the stack is complete.
The first, “concurrent” approach, has drawbacks because, in practice, it is difficult to maintain alignment among the stack components. In addition, it is difficult to ensure that all of the individual connections are each subjected to the appropriate conditions necessary to form reliable interconnections among the constituent components of the stack. Thus, there is a risk that any particular connection will not be made because the conditions near the connection were insufficient or detrimentally in excess of what was required.
The second, “sequential” approach, does not have the alignment problem. However, it still has drawbacks because the heat used to join each chip after the first can adversely affect the connections of previously joined chips.
Thus, there is a need for a better way of joining chips to form a stack that reduces or eliminates the problems that can be encountered by using conventional concurrent or sequential joining techniques.